Borehole Seismic Air-Gun Sources: What’s the Safe Distance from a Ship’s Hull?

摘要

When offshore borehole seismic surveys require the use of arnsupply ship or vessel to position an air-gun source, often thernair-gun source is deployed over the side of the ship. For manyrnyears, this configuration has given concern to ship owners andrncaptains. When conducting borehole seismic surveys, the airgunrnsource is fired several hundred times over the duration ofrnthe survey and there is a fear that the ship may be damaged.rnNow that more powerful gun clusters and arrays are beingrnused, these larger air-gun sources must be positioned furtherrnaway from the ship’s side.rnAn investigation was made of the excitation of the ship’srnhull caused by air-gun firing versus the excitation of the ship’srnhull under sailing conditions.rnThis paper shows how a set of safe distances can bernformulated, so that gun shocks to the ship’s hull whenrnconducting borehole seismic surveys are no worse than hullrnshocks experienced when the ship is sailing under moderaternsea conditions. Recommendations for safe air-gun deploymentrnmethods are presented, so that the safe distance can bernmaintained throughout the borehole seismic survey.